Research On Preparation And Performances Of Oxides And Lithium Titanate Anode Materials For Lithium-ion Battery

As a carrier for electric energy storage,lithium-ion batteries?LIBs?can realize the conversion between chemical energy and electric energy,so as to effectively alleviate the utilization and consumption of the earth's resources.Due to its outstanding performances,it has a wide range of applications.The requirements for the safety performance of LIBs are more stringent because of their penetration into people's daily life.Although the theoretical and practical capacities of titanium dioxide?TiO₂? and lithium titanate(Li₄Ti₅O₁₂) are not as high as that of the commercial graphite,their safety performances are better.As a result,in this paper,the synthesis,doping and composite modification of these two kinds of anode materials were studied by hydrothermal method and solid state method.The main results are as follows:1.Hydrothermal method was chosen to prepare TiO₂ and the effect of hydrothermal reaction temperature on the product was discussed.The galvanostatic test shows that TiO₂sample exhibiting the best electrochemical properties were obtained at 120? hydrothermal reaction temperature.When the corresponding material was used as anode materials,the discharge specific capacities of 269.4,197.7 and 180.5 mAh/g belong to the 1st,3rd and 50th cycles at room temperature,respectively.The capacity retention rate between the 50th and 3rd cycles is as high as 91.3%.On this basis,molybdenum?Mo? doping was carried out and did not change the crystal structure.While the agglomeration degree first improved and then deteriorated with the increase of Mo doping content.Mo doping at 1%is the best.At a current rate of 5 C,the discharge specific capacities of the corresponding material and undoped sample were 75.1 and 17.4 mAh/g,respectively.2.The three-phase composites containing Li₄Ti₅O₁₂,rutile and anatase TiO₂ were also synthesized by hydrothermal method and have irregular nanosheets and nanoparticles morphologies,while pure Li₄Ti₅O₁₂ has an aggregated nanoparticles morphology.The optimum preparation conditions are Li-Ti ratio of 4:5 and heat treatment temperature of600?.122.2 mAh/g was the discharge specific capacity of this composite at room temperature and 5 C rate,while that of pure Li₄Ti₅O₁₂ was only 77.4 mAh/g.The discharge specific capacity of this composite was increased to 143.4 mAh/g at 55? and the same 5 C rate.3.Cationic and anionic doping modifications of Li₄Ti₅O₁₂ prepared by solid-phase method were studied by selecting copper?Cu?and fluorine?F?,and Cu and F substituted Li and O,respectively.The results show that the introduction of Cu will result in the continuous expansion of particle size,even to the micron level.While the increase of F doping content has little effect on the microstructure of the bulk material,but the excessive amount will also lead to a slight increase in the degree of agglomeration of the particles.The optimum doping amounts of Cu and F are x=0.1 and y=0.3,respectively.The first discharge specific capacities at 0.1 C were 162 and 168.4 mAh/g and the reversible specific capacities after 50 cycles were 158.3 and 166.2 mAh/g and the capacity retention rates were 97.72%and 98.69%,respectively.While the corresponding data of the undoped sample were 155.2,151.5 mAh/g and 97.62%,respectively.The discharge specific capacities of Li_3.9Cu_0.1Ti₅O₁₂,Li₄Ti₅O_11.7F_0.3and Li₄Ti₅O₁₂ at a current density of 5 C were 118.5,121.4 and 80.3 mAh/g,respectively.